Environmental safety concerns may arise where a mixing device is used in an industrial mixing process. In this respect, mixing devices using motors (e.g., electric) to provide rotary motion to a mixing impeller will require a conduit seal where the conduit enters a vessel or tank, in order to prevent leakage of vapors, fumes and liquids from the vessel or tank into the motor's power transmission device. Among the different seals used are vapor and umbrella seals for very low pressure, single mechanical seals for vacuum up to pressures to 75 psi, standard stuffing box seals for pressures up to 150 psi, double mechanical seals from full vacuum pressures to 250 psi, and double balanced mechanical seals for pressures above 250 psi. Vapors and fumes may escape from the vessel or tank due to conduit movements which vibrate the seal thus leading to a failure of the seal. Accordingly, a conduit seal requires frequent maintenance and repair, which may result in considerable down-time. A further drawback to conduit seals is that they can be very expensive.
One solution to the problems posed by conduit seals is to eliminate the need for them altogether. In this respect, mixing devices which do not require a motor and gear box, can eliminate the need for conduit seals. Accordingly, mixing devices which provide rotary motion to the mixing impeller by jet action, rather than by a motor and gear box, do not require conduit seals. This jet action is generated by injecting a fluid through nozzles at the tip ends of the impeller. The thrust action of the fluid discharging from the nozzles causes the impeller to rotate.
Prior art jet mixers have relied on fluid discharge from the nozzles as the primary means of mixing the contents of a tank. A rotating blade, paddle or the like may be used as only a secondary means of mixing. Accordingly, prior art jet mixers have provided insufficient mixing action for numerous applications.
Furthermore, prior art jet mixers have relied upon ball bearings in their hub design. Since the hub of a jet mixer may be exposed to various fluids, including corrosive fluids, the ball bearings and the cage housing the ball bearings must be corrosion resistant. One common way to provide a non-corrosive bearing is to use expensive ceramic bearings. Other drawbacks to typical ball bearing designs is the need to periodically clean and lubricate the bearings, the complexity of the hub design, and the high manufacturing costs.
The present invention overcomes these and other drawbacks of prior art devices and provides an efficient, environmentally safe, sealless mixing device.